Tuesday, March 10, 2009

Photography 201

Sometimes things don't go as you expect or hope. A friend e-mailed yesterday afternoon and wanted some pictures of some dynamic message signs (DMS) here in Tampa made by a company in St. Paul, MN called ADDCO. When I looked at what I had in the archives, I had some that looked like the DMS at the left. The words are all garbled! So I went out after work and tried again and got the same results. The sign is working fine, but the picture does not show it. Why? I'm glad you asked. Electronic signs, light bulbs and most electrical appliances operate at 60 Hz (Hertz). Hz are cycles per second that the lights are on an off. Movies have 30 frames (or still pictures) per second but we can tell when one picture ends and the other starts. When we look at the sign with our eyes, we can't see the "off" because our eyes can't adjust that fast. So we see the lights on or smooth motion. The camera in the daylight has a shutter speed of about 1/200th of a second or faster. That means it only lets in light for 1/200th of a second. During that time some of the lights on the sign were "off" so the picture looks goofy. This morning I tried again. This time the camera worked fine. Usually at night, the shutter speed is 1/30th of a second. That allows all the lights to cycle "on" at least once. It also allows your hand to shake a little for a slightly blurry picture. Also the other lights kind of bleed into the surrounding background. These pictures were taken at one of the entrances to the reversible express lanes. I was in the downtown Tampa end. This entrance was closed so the lanes could be reversed for inbound traffic (from the suburbs to downtown). Don't worry, I wasn't standing traffic. There wasn't much traffic and I was standing on a median island when I took these pictures.

I like to drive the express lanes when I can. But since I am not in a carpool any more, the $1.50 each way really adds up. I figure I can save enough to buy at least a tank of gas every other week by avoiding the Expressway. If you don't have a SunPass, the toll fee is $1.75 each way. Using the free highways takes 5-10 minutes longer each way, but that's okay most days. May your life be blessed and your lane be the right pace for you! Love, Steve